Freshwater Pump Sounds Differently When Running

[kusuri]

Hi all -

I've tried searching the forums for this, I couldn't find anything that seemed to match my situation. I've recently purchased a sailboat about a month ago, and my freshwater pump seems to be acting oddly. I have a Shurflow Aqua King II. This week it started sounding differently when it was running.

It used to be a very solid bang-bang sound when running water. Basically it'd bring the pressure to 50 psig in the system, stop running, the pressure would drop to 30 psig, the pump would turn on again and repeat.

Now when it runs it seems to rumble up to 10 psig, hold there for a second, then slowly rumble up to 30 psig and hold there. No bang bang anymore. It seems to be running continuously with a much quieter sound at 30 psig. This would seem like an improvement, but it's the change that's weird to me. The pump delivers water just fine and only runs when I use it.

I'm not sure which operation mode is normal. The bang bang seems more in line with previous sailboat pumps I've used, although the latter is quieter.

What could cause the change and is it a sign of a failing pump? I'll reach out to the manufacturer, but wanted to get insights from you fine people here.

Thank you!

[Bill O]

Would look for a clog before the pump.

If you have a pre-pump filter, check/replace the filter. Look inside the tank to inspect the pick up.

[HeywoodJ]

What you are describing sounds like normal operation for that pump. The Aqua King II has a bypass valve and diaphragm that are supposed to open at 30psi, allowing the pump to run continuously when a tap is opened, and only raise the pressure to the shut off point when all taps/consumers are closed.

The pump operates normally up to about 30 PSI [2.06 Bar], where a spring-loaded by-pass valve opens, allowing flow back from the output side to the input side, providing smooth, steady flow with minimal cycling. As a faucet is opened back up, the pressure will drop, the by-pass will close and full flow is again obtained. This allows good flow, even with today’s restrictive showers and pullout sprayer faucets

The previous operation sounds like the bypass was not operating properly, which can happen if, amongst other things, there is air in the system, which is something that can work itself out and account for the change.

The manual, including a discussion on checking and adjusting the bypass system:https://www.pentair.com/content/dam/...-pumps-iom.pdf

[CaptTom]

I think that unit has four diaphragms. If one of the blows out, it'll act and sound weird. Should be a replaceable part. But, yeah, check for obstructions before or after, and things like a clogged vent on the water tank.

[kusuri]

Thank you everyone! We opened up the pump today and the four membranes were all failing. We replaced them, and it's back to good as new. Really appreciate the insight, folks.

[CaptTom]

Originally Posted by kusuri

Thank you everyone! We opened up the pump today and the four membranes were all failing. We replaced them, and it's back to good as new. Really appreciate the insight, folks.

Glad it worked out. And thanks for the reminder that I should keep a spare membrane on board. Such a simple fix when you have the right part.